PROBLEM TO BE SOLVED: To provide an interdental cleaning instrument of an ISO size 1 or an ISO size 2, which can endure practical use by setting the length of a cleaning part that can be inserted between teeth to be long while sufficiently securing the strength rigidity of the cleaning part by setting the cross-sectional area of a core part to be large.SOLUTION: In an interdental cleaning instrument 1, a soft part 21 for cleaning that is composed of an elastomer is put on and molded at a core part 12 made of a synthetic resin, and a cleaning part 2 to be inserted between teeth is formed by the core part 12 and the soft part 21 for cleaning. The core part 12 is constituted of a core side tapered surface 12a which is reduced in diameter as approaching the distal end side, the cleaning part 2 is constituted of a cleaning side tapered surface 2a which is reduced in diameter as approaching the distal end side, and angles &thetas1 and &thetas2 formed by both tapered surfaces 12a and 2a to the center line L of the core part 12 are respectively set so as to be reduced continuously or stepwise as approaching the distal end side of the core part 12.
